International Correspondence Scbool'l Scranton, Pa.
Elementary Chemistry
PREPARED ESPEClALLY FOR HOME STUDY
By I. C. S. STAFF
5367 EDmON 1 85847 ELEMENTARY CHEMISTRY Serial 53fi Edition
COMPOSITION OF SUBSTANCES
INTRODUCTORY EXPLANATIONS 1. Definition of Chemistry.-Chemistry is the science that treats of the composition of substances and of the changes that affect their composition. 2. Kinds of Substances.-Anything that occupies space CGpJriabt, 19•0. by hTEaHATIONAL TaxTeooK CoMPAifY. Copyright in Great and has weight is known as matter. There are many kinds of Britain. All rigbts re;erved matter. and each kind is a particular substance. Thus. steel, 5367 Printed in U. S. A. iron, wood. stone, water, and air are substances. The Yarious ·- substances are of three general forms. namely, solid. liquid. and 1943 Edition gaseous. A solid substance is one that holds its shape under ordinary cnnditions. For example, iron in its usual form, wood. and stone are solids. A liquid substance is one that has no shape of its own hut takes the shape of the container that holds it. \Yater and oil are liquids. A gaseous substance is one that has no particular shape or volume but tends to fill the container in which it is kept. Air. illuminating gas, and carbon dioxide are gases. The form of a substance can be changed by merely changing the te1pperature of the substance. For example, water, ice. and steam are three forms of the same substance. Ice is obtained by freezing water, and steam is obtained by boiling water; also. either ice or steam can be transformed into water by changing the temperature sufficiently. Similarly. a solid block of steei can be melted. or liquefied, by raising its temperature to a suf ficiently high point. 3. Physical Properties of Substances.-The characteristics or peculiarities by which a substance can be recognized or
C:OP'YRIGHT!:O 8Y 1-NTIEI'HATIO... AL T IXTBOOJ( COM ...\NY . ALL RIGHTS ftES£RVt:O ELE::\IE0ZTARY CHE~IISTRY 2 ELEMENT ARY CHEMIST RY 3 identified or by which it is rendered suitable for a certain pur ordinary temperatures, they will form a mixture. The iron pose are known as the physical properties of the substance. All may be separated from the mixture with a magnet. If, how substances have the general physical properties known as weight ever heat is applied to the mi:
No method has bee~ devised for finding the actual weight of COMPOUNDS an individual atom of an element. However, the relative CHEMICAL FORMULAS FOR MOLECULAR COMPOSITION weights of atoms of the various elements have been determined. 11. Simple Formulas for Compounds.-The composition of These relative weights are called the atomic weights of the ele ments. Slight changes in the accepted values of the atomic a molecule of any chemical compound may be indicated sym weights are made from time to time, in accordance with new bolically by writing side by side the symbols for the various discoveries; but, with few e."
8 ELEMENTARY CHEiviiSTRY ELEMENTARY CHEMISTRY 9 and t he formula for calcium nitrate, which is a compound of In the formula Ca504 • 2H20 for gypsum, the number 2 Ca(N03)2. calcium, nitrogen, and oxygen, is written The ele preceding the symbols H20 means that two molecules of water ments represented by the symbols that are enclosed in paren are combined with the other elements. Such a number is theses form a combination known as a radical. Thus, in the known as a coefficient. ·w hen a coefficient is used, the subscript formula Ca(OH)2, the combination of one atom of oxygen and for each symbol following the coefficient should be multiplied one atom of hydrogen is a radical; and, in the formula Ca(N03)2. by the coefficient in order to determine the total number of the combination of one atom of nitrogen and three atoms of atoms of each element. Thus, in t he formula CaS04 • 2H20, oxygen is a radical. the total number of atoms of hydrogen is 2 X2, or 4; and the A radical is treated as if it were an atom of a single element, total n~mber of atoms of oxygen is the sum of the subscript of 0 and the subscript following the parentheses applies to all the preceding the period and twice the subscript of 0 following symbols in the radical. For example, a molecule of the com the coefficient, or 4+2X1 =6. pound represented by the formula Ca(OH)z contains one atom of calcium and two atoms of each of the elements oxygen and 14. Order of Symbols in Formulas.-There is usually a hydrogen. Similarly, a molecule of the compound whose definite formula for each compound, and the symbols for the formula is Ca(NOa)z contains one atom of calcium, two atoms of various elements that make up the nitrogen, and six atoms of oxygen. The symbols of a radical compound are written in a certain TABLE Il order. T hus, t he formula ~Or water SHORT LIST OF POSITIVE are enclosed in parentheses whenever a subscript is required to 1 ' AND NEGAT IVE ELE MENTS indicate that the radical is contained more than once in the is HzO and not OH2. In most for- Positive Negative molecule and sometimes when there is no subscript. In rel mulas, the order in which the sym Elements Element.s atively simple formulas like KOH for potassium hydroxide and bols are arran6ed is determined by HN03 for nitric acid, no parentheses are needed. the electrical properties of the con K stituent elements, but other factors Cl Na Br 13. Separation of Symbols by Commas or Periods.-The sometimes determine the arrange Ba 0 composition of some compte."'{ compounds may be indicated more ment of the symbols in a formula. Ca I clearly by separating the various symbols into groups by means It is not yet known just what Zn s p of commas or periods. Usually, the symbols in each group takes place when atoms of two or Fe Sn N represent a combination of atoms that are closely related and more elements combine to form Pb c that may be treated as if they constituted a single unit. The molecules of a compound. However, H Si formula for the substance called gypsum is a good illustration it is believed that in every chemical Ag of a chemical formula in which the symbols are divided into reaction the atoms of some elements Au groups by a comma or period. This formula may be written lose electrons and the atoms of other Ca50 , 2Hz0; it may also be written CaSO• . 2H20. Some elements gain electrons. Each atom that loses electrons 4 I chemists prefer to put the period slightly above the bottoms carries an unbalanced positive charge of electricity, and each of the symbols in order to make it more noticeable. Another atom that gains electrons carries an unbalanced negative good illustration of a formula in which the symbols are divided electrical charge. Elements whose atoms tend to lose electrons into groups by a period or a comma is that for manganese sili are said to be electro-pOl'itive, or simply positive; whereas cate, which is a compound consisting of manganese, silicon, and clements whose atoms tend to gain electrons are electro-negative, oxygen. The formula for manganese silicate is Mu02 . Si02• or negative. Some positive elements are more strongly posi- ELEMENTARY CHEMISTRY ELEMENTARY CHEMISTRY 11 10 . than are other positive elements, and some negative all the atoms in the molecule. If there is more than one atom t lVC . ha th . J elements are more strongly negative t n o er negattve e e- of an element in the molecule, the atomic weight of the element must be taken once for each such atom. For instance, since ments. A short list of positive and negative elements is given in Table the formula for water is H~ and each molecule contains two II. The symbols for the elements have been so arranged in the atoms of hydrogen and one atom of ox-ygen, the molecular weight table that the more strongly positive and negative elements of water is equal to twice the atomic weight of hydrogen plus are above those that possess weaker electrical properties. Thus, the atomic weight of oxygen. of the metals shown in the table, potassium may be considered Some of the atomic weights that are given in Table I are the most positive and gold the least positive, while chlorine may expressed to two or more decimal places. In the computations be considered the most negative and silicon the least negative. for certain exact chemical analyses. it may be necessary to use t hese accurate values. However, most of the chemical work in 15. If the fonnulas previously given for compounds con practice is carried out with a degree of accuracy that does not taining only two elements are examined, it will be seen Ullat require using more than one decimal place in any atomic weight the symbols are written in the order of the electrical properties in order to compute the molecular weight of a compound. In of the elements, with the positive element before the negative fact, in most cases, it is accurate enough to express each atomic element. For example, in the formula for common salt, which weight to the nearest whole number. Thus, in determining is NaCl~ the symbol for the positive element sodium is written the molecular weight of water, the atomic weight of hy before the symbol for the negative element chlorine. If both drogen may usually be taken as 1 and that of ox'}•gen as 16. elements are negative, the symbol for the element that is less The molecular weight of water is, therefore, 2X1+16=18. strongly negative is written first. In the case of compounds The number of decimal places, if any, that is to be used in find containing more than two elements, the symbols are often ing the molecular weight depends on the degree of accuracy that arranged according to the electrical properties, with the most is needed. positive element first and the most negative element last. Thus, in the formula Ca(N03)2, the symbol for the positive calcium is EXAMPLE I.-Find the molecular weight of common salt, the formula written first, the symbol for the negative nitrogen is written next, for which is NaCl. and the symbol for the more strongly negative oxygen is placed SoLUTION.-Since a molecule of salt contains only one atom of sodium and one atom of chlorine, the atomic weight of each of these elements is last. However, not all formulas have their symbols arranged used but once. According to Table I, the atomic weight of sodium is according to electrical properties, and there are numerous 22.997, or say 23.0, and the atomic weight of chlorine is 35.457, or say 35.5. formulas in which the symbols for negative elements precede Hence, the molecular weight of salt is 23.0+35.5=58.5. Ans.
those for positive elements. In the fonnula C2H r,OH for a EXAYPLE 2.-What is the molecular weight of the gas known as hydro certain kind of alcohol, the symbol for carbon, which is nega gen sulfide, the formula for which is H,S? tive, is written before the symbol for hydrogen, which is posi SoLUTION.-ln a molecule of hydrogen sulfide, there are two atoms of tive: and the symbol for oxygen also precedes the second symbol ~ydrogen and one atom of sulfur. Since the atorn~c weight of hydrogen for hydrogen. The construction of formulas is the province Js 1.0081, or say 1, and that of sulfur is 32.06, or 32.1, the molecular weight of the chemist and will not receive further consideration here. of hydrogen sulfide is 2X1+32.l =34.1. Ans. . Ex.ul:PLE 3.-Determine the molecular weight of the compound calcium 16. Molecular We ights of Compounds.-The molecular mtrate, the formu~ fo~ which ~s Ca(NO~h; assume that the desired degree weight of any compound, or the relative weight of a molecule of accu:acy perrruts disregarding the decimals in the atomic weights of Qf the compound, is equal to the sum of the atomic weights of the vanous elements. ELEMENTARY CHEMISTRY ELEMENTARY CHEMISTRY 13 12 . -The calculations may be arranged as follows: SoLUTION· CHEMICAL AFFINITY AND VALENCE Atomic weight of nitrogen = 14 3 X atomic weight of oxygen = 48 18. Affinity of Atoms.-It is assumed that each atom of a molecule has a certain attraction for the other atoms of the Atomic weight of radical NOa= 62 molecule. This attraction between at.oms is called chemical Atomic weight of calcium = 40 affinity. 2Xatomic weight of radical = 124 Under favorable conditions there is usually a stronger affinity between atoms of different elements than between Molecular weight of Ca(NOah= 164. Ans. atoms of the same clement. If, however, atoms of different elements are not available under suitable conditions, atoms of 17. Proportions of Elements in Compounds.-The atomic the same kind combine among themselves to form molecules weights of the elements may be used for the pro deter~ining of the element. Thus, two atoms of the gaseous element hydro portions of the ingredients of any compound .. Smce mole eac~ gen unite to form one gaseous molecule of hydrogen, and two cule of common salt contains 23 parts hy wetght of sodlUm to atoms of the gaseous element chlorine unite to form one gaseous 35.5 parts of chlorine, and any larger quantity of salt is merely molecule of chlorine. If the hydrogen and the chlorine gases a collection of molecules, the ratio of the weight of sodium to are mixed, and the mixture is exposed to sunlight, the molecules the weight of chlorine in any quantity of salt is 23 to 35.5. Also, of hydrogen and the molecules of chlorine break up and each since the total molecular weight of salt is 58.5, the proportion atom of hydrogen unites with one atom of chlorine to form a compound that has the formula HCl and is known as hydrogen of the substance that is sodium is ;~ or 39.3 per cent and the 8 5 chloride. The explanation given by chemists for this phe . hl . . 35· 5 60 7 t Similarly, nomenon is that under certain circumstances the affinity between proportion that ts c orme IS _ or . per cen · 58 5 an atom of hydrogen and an atom of chlorine is greater than the the ratio of hydrogen to oxygen in water is 2 to 16; also, -fi of affinity between one atom of hydrogen and another atom of water is hydrogen and H is oxygen. In the case of ferric oxide, hydrogen or between one atom of chlorine and another atom of
the formula for which is Fe,/]3, the proportions of the elements, chlorine. The circumstances under which chemical reactions by weight, are 2X55.8 or 111.6 parts of iron to 3Xl6 or 48 take place are different for different combinations of elements. parts of oxygen. Heat, light, and electricity are some of the agents that are used to cause chemical reactions. EXAMPLES FOR PRACTICE 19. Relatively few of the chemical reactions that take place In the following examples, the atomic weight of each element should be involve the mere combination of two elements to form a com taken to one decimal place. pound. Reactions also occur when two compounds or an ele 1. What is the molecular weight of ferrous sulfide, the formula for ment and a compound are brought together under proper con which is FeS? Ans. 87.9 ditions. In such reactions, the original compounds are broken 2. Determine the molecular weight of calcium carbonate, Co.COa. Ans. 100.1 up and the elements of which they are composed recombine to form new compounds. For example, the affinity of sodium for 3. How many pounds of calcium are contained in 100 pounds of calcium chlorine is much stronger than the affinity of calcium for chlorine. carbonate? Ans. 40 lb. Therefore, if a compound of sodium and one or more other 4. What is the molecular weight of barium hydroxide, Ba(OH).? Ans. 171.4 elements is brought into contact with a compound of calcium
2JJB~• r ELE1\IENTARY CHEMISTRY TABLEID 14 USUAL VALENCES OF ELEMENTS Name o( Element Symbol Valence and chlorine under proper conditions, a reaction takes place. ~ame o( Element !Symbol Valence As a result of this reaction, the sodium combines with the Actinium...... Ac 3* Mercury...... Hg 1, 2 chlorine that was formerly united with the calcium, while the Aluminum...... Al 3 Molybdenum. . . Mo 3,4,6 calcium combines with one or more other elements that were Antimon}'...... Sb 3,5 Neodymium. . . . Nd 3 formerly united with the sodium. In other words, the sod,ium Arsenic...... As 3,5 Nickel...... Ni 2,3 replaces the calcium in the combination with chlorine. Sodium Barium ...... Ba 2 Nitrogen ...... N 3,5 2 Osmium ...... Os 2,3,4,8 also has a much stronger affinity for oxygen than does hydrogen. Beryllium...... Be Bismuth...... Bi 3,5 Oxygen...... 0 2 Therefore, if sodium comes in contact with water, it combines Boron...... B 3 Palladium...... Pd 2,4 with the oxygen in the water and releases the hydrogen. Bromine...... Br 1, 3, 5, 7 Phosphorus..... p 3,5 C.'l.dmium...... Cd 2 Platinum...... Pt 2,4 20. Meaning of Valence.-When atoms of different ele Calcium...... Ca 2 Polonium...... Po 2,4,6* ments unite to form molecules of compounds, they do so in Carbon...... C 2,4 Potassium...... K 1 3,4 Praseodymium. . Pr 3 such a way that the affinity of an atom of each element for atoms Cerium...... Ce Cesium ...... •.. Cs J Protactinium. . . Pa 3,5* of other elements is satisfied. As indicated by the formula HCl Chlorine...... Ct 1,3, s, 7 Radium ...... Ra 2 for hydrogen chloride, the affinity of an atom of hydrogen for Chromium...... Cr 2,3, 6 Rhenium ...... Re 2,4,6, 7• chlorine is satisfied by a single atom of chlorine. Likewise, the Cobalt...... Co 2,3 Rhodium...... RJ, 3 formula NaCl for common salt shows that the affinity of an Columbium ...... Cb 3,5 Rubidium...... Rb 1 1, 2 Ruthenium..... Rn 3,4,6,8 atom of sodium for chlorine is satisfied by one atom of chlorine. Copper...... Cn Dysprosium..... Dy 3 Samarium...... Sm 3 However, when calcium and chlorine combine, they form the Erbium ...... Er 3 Scandium...... Sc 3 compound known as calcium chloride, which has the formula Europium...... Ett 2,3 Selenium...... Se 2,4,6 CaC/ • Fluorine...... F 1 Silicon...... Si 4 2 This formula indicates that it takes two atoms of chlorine to satisfy the affinity of an atom of calcium for chlorine. Gadolinium. . . . . Gd 3 Silver ...... Ag 1 2,3 Sodium ...... Na 1 The combining capacity of one atom of an element, expressed Gallium ...... Ga Germanium. . . . . Ge 4 Strontium...... Sr 2 in terms of the number of hydrogen atoms with which it will Gold...... Ar~ 1, 3 Sulfur...... S 2,4,6 unite or which it will replace, is called the valence of the element. Hafnium ...... Hf 4 Tantalum...... Ta 5 Valence is not a measure of chemical affinity. A simple Holmium ...... Ho 3 Tellurium...... Te 2,4,6 illustration will help to make the distinction between affinity Hydrogen ...... H Terbium ...... Tb 3 1, 3 and valence clearer. As previously stated, chlorine combines Illinium...... ll 3 Thallium ...... Tl Indium...... b' 3 Thorium...... Th 4 with sodium more readily than it does with calcium, because the Iodine...... I 1, 3, 5, 7 Thulium...... Tm 3 affinity of sodium for chlorine is stronger than the affinity of Iridium...... Ir 3,4 Tin ...... Sn 2,4 calcium for chlorine. Nevertheless, one atom of calcium com Iron...... Fe 2,3 Titanium...... Ti 3,4 bines with two atoms of chlorine, whereas one atom of sodium Lanthanum. . . . . La 3 Tungsten...... W 6 combines with only one atom of chlorine. Thus, the valence of Lead ...... Pb 2,4 Uranium ...... U 4,6 Lithium...... Li 1 Vanadium ...... V 5 calcium is twice as great as the valence of sodium. Lutecium...... L" 3 Ytterbium...... Yb 3 The usual valences of the various elements are given in Magnesium...... Mg 2 Yttrium...... Y 3 Table III. As indicated in this table, many of the elements Manganese...... l/11 2,4,6, 7 Zinc ...... Zn 2 have more than one valence. For example, carbon may have a Masurium...... Ma 2, 4, 6, 7* Zirconium...... Zr 4
valence of 2 or 4, and nitrogen may have a valence of 3 or 5. *Valence doubtful. 15
..... ELEMENTARY CHEMISTRY 16 ELEMENTARY CHEMISTRY 17 II The elements helium, neon. argon, krypton, xenon, and r~don t included in the table; these elements are called -r.n.ert For c::arnple, when hydrogen is ignited in the presence of oxygen, arc no . h 'call · h th gases because they do not combme c emt y wtt any o er the two gases will combine in the proportions of two molecules of hydrogen to one molecule of o>..-ygen to form water. The elements. reacti<,n that takes place may be indicated by the equation 21. Application of Valences in Formulas for Compounds. 21I'!.+02=2H20 In a compound that is composed of only two elements, the The part of the equation to the left of the equality sign, valences of the elements show how many atoms of each element or the lcft-h:md member of the equation, shows that originally are contained in a molecule of the compound. If both elements there were two molecules of hydrogen and one molecule of have the same valence, one atom of each will form a molecule oxygen, the sign + being used instead of the word and. Also, of the compound, as in the case of commori salt, NaCl, and the the ~art of the equation to the right of the equality sign, or substance known as quicklime which has the formula GaO. If the n~ht-hand member, shows what is produced by the reaction. the valence of one element is 1 and the valence of the other is 2, In th1s case, the product is two molecules of water. a molecule of the compound contains two atoms of the first In the preceding equation and also in others in this text element and one atom of the second element. For example, the equality sign is used to separate the members of the equation~ the formula for water is H20 and the formula for calcium However, the symbol ~ or P is often used instead of the chloride is CaC~. Similar relations exist in other compounds. equality sign for this purpose. The symbol~ indicates that Thus, each molecule of ferric oxide, Fe203, contains two atoms the reaction between the substances can take place only in the
of iron and three atoms of oxygen; and, since oxygen has a direction shown. For example, the equation BaClt+Na2SOr valence of 2 and iron in this case may be given a valence of 3, BaS04+2NaCl means that barium chloride, BaCh, and sodium the ratio of the number of atoms of iron to the number of atoms suUate, Na~04, will unite to form barium sulfate BaSO and ' 4, of oxygen is the same as the ratio of the valence of oxygen to the common salt, NaCl; but barium sulfate and common salt will valence of iron. There is also a compound of iron and oxygen not combine so as to form barium chloride and sodium sulfate.
which is known as fetTous oxide and has the formula FeO; On the other hand, the equation 2H2+0.P.2H20 means that in this case, the valence of iron is 2. the reaction is reversible, or can take place in either direction. \Vhen a compound is composed of more than two elements, In other words, it is possible either to obtain two molecules of one group of elements is treated as a unit. For example, in water by combining two molecules of hydrogen with one mole calcium nitrate, Ca(N03)2, the radical for which the symbol is cule of oxygen or to decompose two molecules of water so as to N03 is treated as if it were an atom of a single element. The produce two molecules of hydrogen and one molecule of oxygen. valence of the single atom of calcium is 2; and, if the valence of the radical is considered to be 1, the affinity of the calcium for BINARY COMPOUNDS the radical is satisfied. Various other formulas may be analyzed . 23. Types of Binary Compounds.-A compound that con in a similar manner. ststs _of o~ly two elements, or of two groups of elements which act hke smgle elements, is called a binary compound. Each 22. Representation of Reactions by Equations.-The such compound has a distinguishing name which indicates the changes in the composition of substances that take place during composition of the compound. Where the two elements or a chemical reaction can be indicated in a simple manner by groups forming a binary compound can unite in only one way as means of a chemical equation, which consists of the symbols for where each of the two clements has only one valence, it is ;us the elements involved in the reaction and also other symbols. tomary to leave the name of the first element unchanged and to
I'~ ----~------~----~j~------~ ELEMENTARY CHEMISTRY ELEMENTARY CHEMISTRY 18 19 attach the ending ide to the first part of the name of the second is used in the other compound. For example, since iron may t Thus, the chemical name of common salt, NaCl, have a valence of either 2 or 3 and chlorine has a valence of 1, c Iemcn . sodi d hl . . odi . h consists of the elements urn an c onne, 1s s um iron may unite with chlorine to form two different kinds oi w hIC f . li C'aO . cal . chloride; and the chemical name o qwck me, , lS ctwn chlorides. The chloride FeCt,z, in which the valence of iron is 2 oxide. and in which but two atoms of chlorine are present to every atom , In some cases, the same two elements can unite so as to of iron, is called ferrous chloride. The substance FeCl3 in which form more than one compouud. In order to distinguish between the valence of iron is 3 and in which three atoms of chlorine are the different compounds formed by the same elements, the present to every atom of iron, is called ferric chloride. A few ending ide is used for the second element and, in addition, either other examples showing the use of the endings 01£S and ic follow: a further change is made in the name of the second element or a C1l£], cuproz£S oxide GuO, cupric oxide change is also made in the name of the first element. FeO, ferrOZ£S oxide Fe£)3, feriic oxide 24. Elements Uniting in Only One Proportion.-In Table StzC~. stannous chloride SnCl4, stannic chloride IV are shown a few examples of binary compounds of elements CrO, chromous oxide CrzOa, chromic oxide that can unite in only one proportion. These examples serve to illlustrate the method of naming such compounds. In each 26. In the other method that is used to distinguish binary case, the name of the more positive element is given first with compounds formed by elements which may unite in more than out change, and the ending ide is applied to the first part of the one proportion, a prefix is attached to the first part of the name of the less positive or the negative element. name of the negative element. The prefix mono is used where there is one atom of the negative element; the prefix di, or bi, TABLE IV where there are two such atoms; tri, for three atoms; tetra, for NAMES OF BlNARY COMPOUNDS four atoms; and penta, for five atoms. A few examples of the Positive Negative Name of Binary Element Element Formula Compound application of this system follow:
Magnesium Oxygen MgO Magnesium oxide CO, carbon monoxide C02, carbon dioxide Zinc Sulfur Z11S Zinc sulfide S02, sulfur dioxide SOa, sulfur trioxide Potassium Bromine KBr Potassium bromide PCla, phosphorus trichloride PCls, phosphorus pentachlorideo Calcium Carbon CaC, Calcium carbide H20, hydrogen monoxide H202, hydrogen dioxide Sodium Chlorine NaCJ &xlium chloride Hydrogen Sulfur H~ Hydrogen sulfide The prefix per is sometimes applied to the name of the nega Hydrogen Chlorine HCl Hydrogen chloride tive element to show that the greatest possible number of atoms Lead Iodine Pbl, Lead iodide of the negative element is present, as in the following cases: H£)2, hydrogen peroxide, known also as hydrogen dioxide 25. Elements Uniting in More Than One Proportion. Pb02, lead peroxide, known also as lead dioxide There are two ways of naming binary compounds formed by N~02, sodium peroxide, known also as sodium dioxide elements that unite in more than one proportion. In one method, which is generally used if one element is a metal and There is no compound of hydrogen and oxygen in which sometimes if neither is a metal, the ending 01£S is added to the there is a greater proportion of the negative element than in first part of the name of the positive element in the compound hydrogen peroxide. The same fact holds true for all other in which that element has the lower valence and the ending ic binary compounds in which the prefix per appears. Good ELEMENTARY CHEMISTRY ELEMENTARY CHEMISTRY 21 20 TABLE V examples of substances that are nam~ acc~rding t~ the nomen clature here explained are the followmg oXIdes of mtrogen: METALS AND NON-METALS
N,P, nitrous oxide Metals Non·Metals NO, nitric oxide Names Names N 20 3, nitrogen trioxide :-;ames , N02 or N 20 4 nitrogen dioxide or nitrogen tetroxide - Molybdenum Argon N 0 , nitrogen pentoxide Actinium 2 5 Neodymium Arsenic Aluminum Boron The prefix sesqui is sometimes added to the name of the Antimony Nickel Bromine negative element to denote that there are ll atoms of the nega Barium Osmium Carbon tive element to every atom of the positive element. For Beryllium Palladium Platinum Chlorine example, ferric oxide, F e£Ja, is sometimes called iron sesquioxide. Bismuth Cadmium Polonium Fluorine Calcium Potassium Helium ACUDS, BASES, AND SALTS ' Cerium Praseodymium Hydrogen Iodine 27. Definitions.-The definitions of the terms acid, base, Cesium Protactinium Krypton and salt are so intenelated that one depends on the other. Chromium Radium Rhenium Neon Also, the term metal is used in each of the definitions. There Cobalt Columbium Rhodium Nitrogen fore, in defining these terms, it is necessary to make use of Oxygen Copper Rubidium Phosphorus terms that have not yet been defined and the definitions may Dysprosium Ruthenium Radon not be clear until all have been read. Erbium Samarium A metal is an element that forms a basic hydroxide and can Europium Scandium Selenium Silicon replace hydrogen in acids so as to form a salt. Iron, copper, Gadolinium Silver Gallium Sodium Sulfur zinc, tin, and lead are typical metals. Germanium Strontium Tellurium An acid is a substance that contains hydrogen which may be Gold Tantalum Xenon replaced by a metal and that also changes the color of the Hafnium Terbium vegetable dye known as litmus from blue to red. CommonJy Holmium ThaUium Thorium known acids are hydrochloric acid, HCl; sulfuric acid, Hz,S04 ; Illinium Indium Thulium and nitric acid, HNOa. Iridium Tin A base is a compound of a metal and the radical that consists Iron Titanium of one atom of oxygen and one atom of hydrogen. Such a Lanthanum Tungsten compound is also known as a hydroxide, or a basic hydroxide. Lead Uranium Examples of hydroxides are sodium hydroxide, NaOH; cupric Lithium Vanadium Lutecium Ytterbium hydroxide, CH(OH) ; and ferric hydroxide, Fe(OH)3. 2 Magnesium Yttrium A salt is a substance that is formed when some or all of the Manganese Zinc hydrogen atoms of an acid are replaced by atoms of a metal. Masurium Zirconium Mercury 28. Metals and Non-Metals.-On the basis of the definition of a metal given in the preceding article, the elements that are ELEMENTARY CHEMISTRY 23 22 ELEMENTARY CHEMISTRY
usually considered metals and the elements that are non In a similar manner, the acid that has the formuJa H.;504 metals are listed in separate groups in Table V. However, the is called sulfuric acid; and the acid having the formula HN03 is dividing line between metals and non-metals is not a sharp one, called nitric acid. and some elements act as metals in some compounds and as According to another system of naming acids, the various non-metals in other compounds. Examples of such elements chlorine acids would be designated in Lhe following manner: are aluminum, antimony, manganese, selenium, and tellurium. HCl, hydrogen chloride Metals are generally electro-positive elements, and non HClO, hydrogen hypochlorite metals are electro-negative elements. When in compact form, HCl02, hydrogen chlorite a11 metals have what is known as metallic luster. However, HCl03, hydrogen chlorate when in powdered form, most metals appear black, the excep HCl04, hydrogen perchlorate tions being aluminum and magnesium. Acids containing oxygen are called oxyacids. The portion 29. Names of Acids.-It is possible to form several different of an oxyacid that combines with the hydrogen is called the acids by combining a non-metallic element with hydrogen alone negative radical for the acid. For example, 504 is the negative and also with hydrogen and various proportions of oxygen. radical of sulfuric acid and N03 is the negative radical of nitric In ord{:r to distinguish between the acids of a given element, acid. various prefixes and suffixes are applied to the first part of the name of that element. One system used in naming acids is as 30. · Properties of Acids.-If an acid is allowed to react given for the following series of acids in which chlorine is the with a metallic element, the elements that were originally com characteristic element: bined with hydrogen in the acid will combine with the metal instead and the hydrogen will be set free. For example, if a HCl, hydrochloric acid piece of zinc is placed in hydrochloric acid, the zinc combines HClO, hypochlorat4S acid with the chlorine to form zinc chloride, ZnCL2 , and the hydrogen HCl02, chlorot'-S acid is released in the form of a gas, as indicated by the equation HCl03, chloric acid HCl0 , perchloric acid 4 Zn + 2HCl One acid of the series is considered the principal acid and . . hydrochloric zinc zmc + .d = hl 'd + hydrogen its name is given the ending ic, as chloric acid for HCl03• The ac1 c on e name of the next acid, which contains less oxygen than the
principal acid, takes the ending OtiS, as chlorous acid for HCl02 • An arrow pointing upward is sometimes used in an equation to For the next acid, which contains less oxygen than the acid whose indicate that the substance whose symbol it follows tends to name ends in OtiS, the name takes the prefix h·ypo and the end escape into the air as a gas. Acids are the only compounds of ing OilS, as hypochlorous acid for HClO. The acid that con hydrogen that can react with metals so as to form a salt and tains only hydrogen and the characteristic element is named release the hydrogen. with the prefix hydro and the ending ic, as hydrochloric acid When used for practical purposes, acids are generally in the for HCl. If there is an acid in the series that contains more form of solutions, which are prepared by dissolving the com oxygen than the principal acid, its name takes the prefix per pounds in water. Thus, the familiar form of hydrochloric
and the ending ic, as perchloric acid for HCl04• acid is a solution consisting of water and a known proportion ELEMENTARY CHEMISTRY 25 24 ELEMENTARY CHEMISTRY of hydrogen-chloride gas. An important property of every acid color becomes less distinct; and at a certain point the color of is that a solution containing an acid can change the color of the solution, while still blue, becomes slightly reddish. At about this point the solution is neutral, or is neither alkaline litmus from blue to red. nor acid, because th~ alkali and the acid have neutralized, or 31. Bases and Alkalies.-Bases, or hydroxides of metals, destroyed, the properties of each other. Similar results are are combinations of oxides of metals with water. For instance, obtained with other acids and alkalies. The general process of sodium hydroxide, NaOH, is a combination of sodium oxide, destroying the alkaline or acid properties of a solution by allow Na 0, and water, as indicated by the following equation: ing an alkali and an acid to act on each other is known as neu 2 tralizaticm. Na20 + H20 = 2NaOH 33. Classes of Salts.-The substances that conform to the sod~um + water = sodi~ oxtde hydrox1de chemica~ definition of a salt may be divided into four classes, which are known as normal salts, acid salts, basic salts, and The oxides of some non-metaUic elements do not form hydrox mixed salts. "Whenever a base and an acid react, the products ides, or bases, when they combine with water, but form oxy of the reaction are a salt of some kind and water. A 1wrmal acids instead. For example, salt is a salt that is produced when all the hydrogen atoms in the acid are replaced by atoms of the metal that were formerly SOa + H20 = H;504 present in the base. For example, potassium hydroxide may sulfur sulfuric + _ react with sulfuric acid in the manner indicated by the follow tnox1. "d e water- act.d ing equation:
Oxides of metals that form bases when combined with water 2KOH + HS04 = KSO" + 2H20 are called basic oxides. Bases, like acids, are usually dissolved potassium sulfuric potassium in water for practical use. hydroxide + acid = sulfate + water Some bases, when in the form of a solution in water, will The potassium sulfate, KiSO"' is a normal salt, because all the change the color of red litmus back to blue. Such bases are hydrogen atoms in sulfuric acid are replaced by potassium atoms known as alkalies. Examples of alkalies are sodium hydroxide, in the salt. NaOH, and potassium hydroxide, KOH. An acid salt is a salt that is produced when only some of the hydrogen in the acid is replaced by atoms of the metal that were 32. Neutralization.-If two or three drops of a solution formerly in the base. Another possible reaction between of hydrochloric acid is added to a solution of litmus in pure potassium hydroxide and sulfuric acid is indicated by the equa water, the color of the solution is changed from blue to bright tion red. If, now, a few drops of a solution of sodium hydroxide is KOH + H;504 = KHSO" + H20 added to the reddened litmus solution, the original blue color is . sulf . potassium restored. By adding sufficient acid, the color of the solution pota ss1um unc .d + .d = hydrogen + water may again be changed to red. When the red color is obtained, h y droxt e act sulfate the solution is said to show an acid reaction; and, when the blue color is restored, it shows an alkaline reaction. As acid is The potassium hydrogen sulfate, KHS04, is an acid salt, because gradually added to a blue solution containing litmus, the blue it contains one of the hydrogen atoms of the acid. ELEMENTARY CHEl\IIISTRY 26 ELEMENTARY CHEMISTRY 27
A basic salt is a salt that results when the base is only partly KClO, potassium hypochlorite; formed from HClO, hypo neutralized by the acid, as in the reaction indicated by the chlormiS acid or hydrogen hypochlorite.
equation KCL02, potassium chlorite; formed from HCL02, chlorous acid or hydrogen chlorite. · Z11(0Hh + HCl KCl03, potassium chlorate; formed from HCl0 , chloric acid . h dr hi . zinc 3 zmc + y oc one h · or hydrogen chlorate. hydroxide acid = ydroxy- + water chloride KCl04, potassium perchlorate; formed from HCl04 , per chloric acid or hydrogen perchlorate. The zinc hydroxy-chloride, Zn(OH)Cl, is a basic salt. As explained before, the name of any salt consisting of only A mixed salt is a salt that is produced when the hydrogen two elements ends in ide, even though the name of the acid used atoms of an acid are replaced by atoms of two different metals. in producing the salt has the prefix hydro and the ending ic; In such a case, the acid first reacts with one base to form an acid thus, KCl is called potassium chloride. The name of a salt salt and water, and the acid salt then reacts with another base formed by a metal and the negative radical of an oxyacid whose to form the mixed salt and water, as indicated by the following name ends in om has the ending ite, as potassium hypochlorite equations: for KClO and potassium chlorite for KCl02• Also, the name KOH + H.,SO. = · KHSO. + H20 of a salt consisting of a metal and the negative radical of an oxyacid whose name ends in 1·c has the ending ate, as potassium and KHSO. + NaOH = I<.NaS04 + H 10 chlorate for KClOa and potassium perchlorate for KCL0 • The potassium sodi potassium 4 prefix hypo or per appearing in the name of the oxyacid is hydrogen h dr W:Od = sodium water + + retained in the name of the salt. sulfate Y OXl e sulfate Salts whose metal parts, or positive elements, are elements A mixed salt is also called a dmwle salt. that exhibit more than one valence are named in the manner A normal salt or a mixed salt is neutral as far as its effect on described for binary compounds whose positive elements have litmus is concerned; that is, the salt will not change the color more than one valence. The names of such elements take the of a litmus solution. As their names imply, an acid salt turns a ending ous when the elements have the lower valence, and the litmus solution red and a basic salt turns such a solution blue. ending ic when the elements have the higher valence. For The metal part of a salt is called the positive radical of the salt , example, St1S04 is called stannous sulfate and Sn(S04) 2 is and the acid part is the negative radical. stannic sulfate.
34. Names of Salts.- The names of salts are determined by 35. Acid salts that are obtained from an acid which can the names of the acids from which they are formed. The form only one acid salt with a given metal may be named in method may be illustrated by the names of the different salts any of the following three ways: the term hydrogen is used after that are formed when potassium hydroxide reacts with the acids the name of the metal; the term acid is used before the name of of chlorine. These salts and their names are as follows: the metal; or the prefix di or bi is applied to the name of the negative radical. Thus, the salt that has the formula KHS04 KCl, potassium chloride; formed from HCl, hydrochloric acid is called potassium hydrogen sulfate, acid potassium sulfate. or or hydrogen chloride. potassium disulphate. 29 28 ELEMENTARY CHEMISTRY ELEMENTARY CHEMISTRY Some acids form more than one acid salt with the same metal. stood that water is the solvent. A solution in which water is For instance, when sodium hydroxide, NaOH, reacts with phos the solvent is known as an aqueous sol1ttion. phoric acid, H3PO.! the possible reactions are as follows: NaOH+H3P04=NaH2P04+H.JJ 37. Suspensions , Colloidal Suspensions, and Emulsions. 2NaOH+H3P04=N~P04+2H20 In some cases, a finely divided solid is dispersed through a liquid without being dissolved by the liquid. Thus, water may carry 3NaOH+H3PO.=Na3P04+3H.JJ fine sand in suspension. The solid material usually imparts a In each of the first two reactions an acid salt is formed, and cloudy appearance to the liquid. Also, if the mixture is allowed in the third reaction a normal salt is produced. These acid to stand long enough, the solid particles will eventuaiJy settle salts can be distinguished by designating either the number of t o the bottom of the liquid. The solid particles are therefore hydrogen atoms or the number of sodium atoms in each. Thus, I said to be in suspension in the liquid, and the mixture is called NaH?O.. is called either dihydrogen sodium phosphate or a suspension. monosodium phosphate; and N~P04 is called monohydrogen Occasionally, the solid is so finely divided that it does not sodium phosphate or disodium phosphate. The normal salt make the liquid noticeably cloudy and does not settle out in a Na~04 is called sodium phosphate or trisodium phosphate. reasonable length of time, and yet is not actually dissolved in In the case of a basic salt, the term hydroxy is used after the the liquid. T he mixture is then ca11ed a colloi~al sus~ension name of the metal, as in the name zinc hydroxy-chloride for or a colloidal solution, and the solid is called a co1J01d. M1xtures the salt whose formula is Zn(0 H)Cl. A mixed salt is designated of starch, glues, and gums with water are examples of colloidal by naming both metals, as in the case of potassium sodium suspensions. . . . sulfate, KNaS04• When a liquid is suspended throughout another liqwd m _the SOLUTIONS AND THEIR IONIZATION form of minute drops, the mixture is called an emulswn. SOLUTIONS Common examples of emulsions are milk and also mixtures_of 36. Nature of Solutions.-One substance is said to be dis oil and water. In time, the constituents of an emuls10n solved in another substance if the two substances when mixed separate. do not combine chemically but are so intermingled in a finely divided state that they form a homogeneous mass and will not 38. Amount of Solute in Solution.-If two liquid~ form a separate no matter how long the mass is allowed to stand. The solution rather than an emulsion when they are nuxed, an mixture that is obtained when one substance is dissolved in unlimited amount of either liquid can be dissolved by the another is called a solution. Thus, if a quantity of common other liquid. However, there is a ~t _to _the amount of a salt, NaCl, is mixed with water, the salt dissolves in the water solid or a gas that can be dissolved m a hqutd. When a solu and a solution is obtained. The substance that is dissolved is tion contains all of the solute that can be ~ssol ve~ by t~e known as the soltite, and the substance in which the solute is solvent and further additions of the solute will r~tn undis dissolved is called the solve1~t. Solutes may be solid, liquid, or solved, the solution is known as a saturated solut1on. T he gaseous in form before they are placed in the solvent. With amount of solute that can be dissolved usually depends o~ the · few exceptions, solvents are liquids, but it is possible to dissolve temperature, as a greater amount can be dissolved at a higher one solid in another solid or to dissolve one gas in another gas. temperature than at a lower tempe~ture. . The most common solvent is water and, where the term solu A solution that contains a relattvely small . pro~orhon of tion is used without giving the name of t he solvent, it is under- the solute, whether or not it is a saturated solutton, lS called a
BB 211B-3 ELEMENTARY CHEMISTRY 31 ELEMENTARY CHEMISTRY 30 A molar solution is an aqueous solution in which the number dilute solution. A solution containing a relati~ely large pro of grams of solute in a liter of solution is equal to the molecular portion of sol~te is know~ a~ a concentrated so_luttOn. The term weight of the solute. Thus, a molar solution of sodium c~oride collcentratiol~ ts used to mdicate the proport10ns of solute and contains 58.5 grams of solute per liter, and a molar solut10n of solvent in a solution. These proportions may be expressed calcium nitrate contains 164 grams of solute per liter. by the weight of solute ~n a certain weight or vo~ume of sol ut~on; by the ratio of the wetght of solute to the wetght of solution; 40. Crystallization, Dehydration, and Efllorescence.-As or by the equivalent fraction, decimal, or per cent. If the previously stated, a saturated solution can contain less of the ratio of the weight of solute to the weight of solvent is very solute when the temperature of the solution is lowered. There small, the proportions may be expressed in parts per miUion, fore, if a saturated solution of a solid substance in a liquid is which is the number of units of weight of solute in a million allowed to cool, some of the solute will separate from the solu units of solution. Thus, when water is analyzed, the amount tion in the form of crystals, which are bodies with definite shapes. of each substance dissolved in it is given in parts per million. This process of separation is known as crystallization. Each The removal of some of the solvent in a solution by evapora molecule of these crystals is usually composed of the original tion or other means is called concentrating the solution. If solute and one or more molecules of water. For example, all the solvent is evaporated, the solution is said to be evaporated crystals of copper sulfate have the formula CuSO• . 5Hz0 and to dryness. The only method of separating a solid solute from crystals of ferrous sulfate have the formula Fe504. 7 H20. The the solvent in a solution is by evaporating to dryness. water in crystals is called water of crystaUization, and a substance that contains such water is called a hydrate. There are also 39. Normal and Molar Solutions.-Metric units are gen crystals without water of crystallization. . erally employed in chemical work. If the concentration of a Water of crystallization may be driven off by heatmg the solution is expressed by weight of solute in a certain volume of crystals. This process is called dehydration; and the remain solutidn, it is usually given as the number of grams of solute in ing substance is said to be in the ank}'drott.s form. For example, either a liter or 100 milliliters of solution. A normal solution if heat is applied to plastic clay, or kaolin, which has the formula is an aqueous solution in which the number of grams of solute • • Al.J)3 Si02 iH~. the water of crystallization is driven off. in a liter of solution is equal to the molecular weight of the solute The anhydrous form may be brick, porcelain, or some other divided by the product of the number of atoms and the valence similar substance, the character of the product depending on of the posit ive element or radical in the solute. In the case of the proportions of aluminum and silicon in the ori~n~ clay. sodium chloride, NaCI, there is one atom of the positive ele Some crystals gradually lose their water of crystallizat10n on ment sodium and its valence is 1; and the number of grams of exposure to the air and usually tum into a powdery substance; solute in each liter of a normal solution is equal to the molecular this process is known as efflorescence. The name ~orescence weight 58.5. For calcium nitrate, Ca(N03) 2, the molecular is also applied to the powdery substance that remams. weight is 164, there is one atom of the positive element calcium, and its valence is 2; hence, a liter of a normal solution contains 41. Distillation and Deliquescence.-A so1ven~ ~n. be 164+2=82 grams of solute. For sulfuric acid, H.S04, the separated from a solution by the proces~ kno~ as distillat~on . number of grams of solute in a liter of a normal solution would In this process, the solution is heated m a suttable c?n~mer be found by dividing the molecular weight 98 by 2, because so as to evaporate the liquid, and the vapor or gas that ts ~tven the product obtained by multiplying the two atoms of hydro off is collected in a separate container and is condensed or bque- gen by its valence of 1 is 2. ELEMENTARY CHEMISTRY ELEMENTARY CHEMISTRY 33
fied. The condensed vapor is called the distillate, and the sub of an atom or a radical that has either gained or lost one or stance that remains in the original container is the reS1atte. more electrons. An ion that is formed by the addition of There is always some moisture in the air, and certain sub electrons gains a negative electrical charge and is called a stances will absorb such moisture. These substances are said negative ion, or an a1~ion. On the other hand, an ion that is to be Jz,•groscopic. Many hygroscopic substances will dissolve formed by the loss of electrons loses ·a negative electrical in tbe moisture they absorb from the air, and this dissolving charge and is a positive ion, or a cation. process is called deliquescence. The principles underlying .the formation of ions may be illustrated by the combination of sodium and chlorine to form 42. Precipitation.-When two solutions with different t· the salt sodium chloride, NaCl, and the solution of the salt in solutes are mixed, a chemical reaction may take place between water. When the sodium combines with the chlorine, an elec the solutes, and one of the substances that is produced by the tron is transferred from each atom of sodium to the atom of reaction may be insoluble or only slightly soluble in water. The chlorine ~th which it unites. In other words, each sodium insoluble product of the reaction will then become visible ' atom is converted into a positive sodium ion, while each chlorine as a solid that is suspended in the liquid. Such a solid is called atom is converted into a negative chlorine ion. When sodiu.n a precipitate, and the process by which the precipitate is formed chloride is dissolved in water, some of the molecules of the salt is known as precipitation. A precipitate tends to settle to the are decomposed into dissociated sodium ions and chlorine ions. bottom of the vessel containing it and thus to separate from the liquid. 44. Symbols for Ions.- The decomposition of a molecule of An example of the formation of a precipitate is the reaction sodium chloride into a sodium ion and a chlorine ion may be indicated by the following equation: indicated by the equation NaCl=Na++Cl- 2NaOH + CuCl2 ---t C1t(OH)2 l + 2NaCl In the case of a solution of sulfuric acid, a molecule of which is sodium cupric cupric + sodium hydroxide + chloride = hydroxide chloride decomposed into two hydrogen ions and an ion of the radical 504, the equation is An arrow pointing downward is sometimes used in an equation HS04 =2H++S04= to indicate that the product whose formula it follows is a precipi Also, the decomposition of a molecule of ferric chloride into a tate. Thus, if solutions of sodium hydroxide and cupric chloride ferric ion and three chlorine ions is indicated by the equation are mixed, the chemical reaction that takes place produces FeCl3 =Fe++ ++3CL- cupric hydroxide and sodium chloride; the cupric hydroxide is In each case, an ion is represented by writing the symbol in the form of a precipitate and the sodium chloride becomes the for the atom or radical from which the ion is formed and plac solute in a solution. ing above and to the right of that symbol one or more small IONIZATION plus or minus signs. Plus signs are used for positive ions, and 43. Ions.-When a compound that is formed by the minus signs for negative ions. The number of such plus or transfer of electrons from the more positive element or radical minus signs is equal to the number of electrons that are lost to the more negative element or radical is dissolved in water, or gained by the atom or radical in the fonnation of the ion. there is a tendency for some of the molecules to be decomposed This is likewise the valence of the atom or radical. Where there into electrically charged particles called ions. An ion consists is more than one plus sign, the several signs are placed side by 34 ELEMENTARY CHEMISTRY ELEMENTARY CHEMISTRY 35 side, as shown for the ferric ion. Two or more minus signs are than a value of 6.6. A pH value between 7 and 14 indicates placed in a vertical column, as shown for the ion of the radical alkalinity, the pH value increasing as the degree of alkalinity so~. which has two such signs. The number of ions is indicated increases. by the numerical coefficient that precedes the symbol for the atom or radical. Thus, 2H+ means two hydrogen ions and 46. Electrolysis.-There are many solutions that will con 3Ct- means three chJorine ions. Each ion of hydrogen or chlo duct· an electric current, and these solutions are known as rine has a deficiency or an excess of only one electron, and there electrolytes. The term electrolyte is also applied to the solute fore only one plus or minus sign is used. in the solution. If two plates or rods of suitable materials, such as metals or carbon, are connected to a source of electricity 45. Hydrogen-Ion Concentration and pH Value.-Even in and are inserted in an electrolyte, the electric current will flow pure water, there is some dissociation of molecules into Ions, as through the liquid from one plate or rod to the other. The indicated by the equation plates or rods that are used for passing an electric current H£J=H++OH- ' ' through an electrolyte are known The positive ions are the hydrogen ions, and the negative ions as electrodes. As the current are ions of the radical OH, or hydroxyl ions. passes through the liquid, it de In pure water or a neutral solution, the number of hydrogen composes the molecules of the ions is equal to the number of hydroxyl ions. When a solution electrolyte into ions. The de has an acid reaction, the concentration of the hydrogen ions composition of a compound by exceeds that of the hydroxyl ions. On the other hand, when a means of an electric current is solution has an alkaline reaction, the hydroxyl ions predominate. called electrolysis. For practical purposes, it may be assumed that the product of A simple apparatus for electrol a ysis is shown diagrammatically the hydrogen-ion concentration and the hydroxyl-ion concentra Copper tion in water or a very dilute solution is a constant. Therefore, in Fig. 1. The vessel a contains Sulfate a measure of the hydrogen-ion concentration is really also a an electrolyte b, which in this measure of the hydroxyl-ion concentration. case is copper sulfate, CuS04. FiG. 1 The hydrogen-ion concentration in water is so small that The electrodes c and d, which if this concentration were expressed as a simple decimal: here consist of a copper bar and a carbon plate, respectively, there would be several ciphers between the decimal point and are submerged in the electrolyte and are connected to the termin the first other figure. In order to avoid the use of such deci als of an electric generator e. As the current passes through the mals, it is convenient to express the hydrogen-ion concentration electrolyte, the copper sulfate is dissociated into positive C1tions by means of a number which is between 0 and 14. T his number and negative 504 ions. is called the pH value. The pH value of water or any solution indicates whether the liquid has an acid or alkaline reaction and 47. Electroplating.-The electrode from which an electric also shows the degree of acidity or alkalinity of the liquid. A current flows into an electrolyte in an apparatus like that shown. neutral liquid, like distilled water, has a pH value of 7. A pH in Fig. 1 is called the positive electrode, or anode; and the value between 0 and 7 indicates acidity, the degree of acidity electrode into which the current flows from the electrolyte is being less for a higher pH value than for a lower value. For the negative electrode, or cathode. In the illustration, the in.c;tance, a pH value of 5.8 indicates a greater degree of acidity copper bar c is the anode and the carbon plate d is the cathode. ELEMENTARY CHEMISTRY ELEMENTARY CHEMISTRY 37 36
1 Jectricity, positive charges attract negative charges, n egative charges attract positive charges. Also, positive and ne . . . es repel other pOSttlve charges, and negatlve charges repel cargh f h .. . . other negative charges. There ore. t e posttlve 10ns, or catto~, PROPERTIES OF SUBSTANCES roduced by electrolysis tend to collect on the cathode, while fhe negative ions, or anions, tend to collect on the anode. Each NON-METALLIC ELEMENTS AND THEIR COMPOUNDS positive Ct~ ion that i~ p~oduce~ b~ the elec~rolysis of copper GASEOUS NON-METALLIC ELEMENTS sulfate in the manner mdicated 10 Ftg. 1 acqwres two electrons from the cathode so as to become a normal atom of copper and 48. Hydrogen.-Hydrogen is a colorless, odorless, and taste attaches itself firmly to the cathode. In this manner, a coating less gas. Its molecular weight is less than that of any other of metallic copper is deposited on the cathode. Each negative element and it is, therefore, the lightest substance known. It so. ion from the copper sulfate loses two electrons to the anode is inflammable and burns with a colorless flame, the product of and combines with an atom of copper in the anode to form a the combustion being water. Hydrogen is Of!.ly slightly soluble molecule of copper sulfate. The molecules of copper sulfate in water. thus produced go into solution in the electrolyte and the con Hydrogen occurs infrequently in the free condition; in some centration of the copper-sulfate solution is thus kept practically localities it issues from the earth in small quantities. Its chief constant until the entire copper bar c is consumed. occurrence is in combination with oxygen in water. Also, it is The process of coating a material with a metal by means of combined with carbon and oxygen or with carbon, oxygen, and an electric current is known as electroplating. Several metals nitrogen in most animal and vegetable matter; and it is a con are suitable for electroplating, and the process is often desig stituent of petroleum, coal, natural gas, and other substances nated more specifically by the name of the metal that is used. known as hydrocarbons. Thus, the process is called copper-plating, nickel-plating, silver plating, etc., to indicate the metal that is deposited. The met:aJ 49. Oxygen.-Like hydrogen, oxygen is a colorless, odorless, to be used as the coating must be an ingredient of the solute and tasteless gas. Oxygen occurs abundantly in nature, both in the electrolyte and must also be the material of which the in the free state and in combination with nearly all other ele positive electrode is composed. ments. It occupies about one-fifth of the volume of air, in which it is mixed, but not combined, with nitrogen and very sma.ll percentages of the inert gases and impurities such as carbon dioxide. In its combined form, oxygen constitutes, by weight, eight-ninths of water and nearly one-half of the earth's solid crust. Oxygen does not bum, but it supports the combustion of other substances. It is slightly soluble in water, and water usually contains some dissolved oxygen.
50. Chlorine.-Chlorine is a greenish-yellow gas that is extremely irritating to the mucous membrane and is poisonous. It is readily soluble in water. Also, it has a great affinity for hydrogen, with which it forms hydrochloric acid, and for most ELEMENTARY CHEMISTRY 38 ELEMENTARY CHEMISTRY 39 "th which it forms chlorides. The most common mcta~ds, Wlare sodium chloride (common salt), NaCl; calcium in water, and the concentrated hydrochloric acid of commerce chlon es . · M c~- Chi · · Cl · and magnesiUm chlonde, g "2· onne ts is an aqueous solution that contains about 38 per cent of hydro chlonde,. ca :t. . • a very efficient dtsmfectant. gen chloride. Hydrochloric acid is also known as muriatic acid. This acid has a characteristic odor and gives off dense fumes 5l. Nitrogen.-Nitrogen is colorless, odorless, and taste when the stopper is removed from a bottle in which it is kept. less. In its free state, it constitutes nearly four-fifths of the It is a very strong acid and is poisonous. volume of air; and, in combination with hydrogen, ca~bon, and m;ygen, it is a constituent of many vegetable and ammal sub , 55. Nitric Acid and Ammonia.-Pure nitric acid, HN03 is stances. Nitrogen is incombustible and does not support co~ colorless; but nitric acid usually has a faint yellow tinge, because bustion. It combines with only a few other elements, but 1ts it contains impurities and becomes partially decomposed. It compounds include strong acids, violent explosives, and active has a characteristic odor and is fuming. Also, it is strongly poisons. acid and is corrosive. In contact with vegetable substances like cotton and sugar, it forms compounds that are violently 52. Fluorine.-Fluorine is a colorless gas that has a .strong explosive. All the metals that are in common use with the affinity for other elements; it even attacks glass. The presence exception of gold, platinum, and aluminum, can be di~olved by of relatively small amounts of fluorine in drinking water is nitric acid. Gold can be dissolved by aq1ta regia, which is a injurious to the teeth of children. The most important com miKture of hydrochloric and nitric acids. pound of fluorine is the mineral known as calcium fluoride, or Ammonia, l'•:H3, which is a compound of nitrogen and hydro jlttorspar, CaF2• In the manufacture of iron and s~el, fl~~r gen, is a pungent gas that is easily liquefied. It dissolves spar is useful as ajlt1x, or a substance that causes the 1mpuntJes readily in water to form ammonium hydroxide, as indicated by to remain liquid at a comparatively low temperature. the equation COMPOUNDS OF GASEOUS NON-METALLIC ELEMENTS NHa + H20 = NH40H 53. Water.-The formula for water is H.f), each molecule . ammonium ammonm + water = h dr .d of water containing two atoms of hydrogen and one atom of y OXl e oxygen. Water can be formed by mixing hydrogen and oxygen The radical NH~. which is a positive radical, is known as and igniting the mixture, preferably by means of an electric the ammonium radical. A common ammonium salt is sal current. A violent explosion accompanies the reaction. It is am11wniac, or ammonium chloride, NH4Cl. also possible to decompose water into hydrogen and oxygen by electrolysis. 56. Oxidation atid Reduction.-In its narrow sense, oxida In its liquid form, water is a powerful solvent, there being tion means the comparatively slow union of oxygen with another comparatively few substances that are not dissolved in water to element. For example, the rusting of iron to form ferric oxide at least a small extent. Therefore, chemically pure water is is a case of oxidation. Similarly, reduction might be limited to usually obtained by distillation. Water unites with most oxides mean the removal of oxygen. However, it is now customary to to form either acids or bases. give a broader meaning to oxidation and reduction. Oxidation 54. Hydrochloric Acid.-In its gaseous state, hydrogen may be defined as either illcreasing the proportion of the nega chloride, HCL, is colorless and pungent. It is readily dissolved tive radical or decreasing the proportion of the positive radical of a compound. Reduction is the reverse, and it means either ELEMENTARY CHEMISTRY ELEMENTARY CHEMISTRY 41 40 reducing the proportion of the negative radical or increasing the The diamond is the hardest of all known substances. There proportion of the positive radical. Every reaction that involves fore, diamonds are employed for cutting substances like glass oxidation also involves reduction. A few reactions involving and as cutting edges on certain kinds of rock drills. The dia oxidation and reduction are indicated by the following equations: monds so used are smaller and much less expensive than those used as gems. 4Fe+302=2Fe~3 Graphite is much softer than the diamond. The finer grades 2FeCh.+Ch. = 2FeCla of graphite are used in the manufacture of lead pencils. The Zn+ 2HCl =ZnCh+ H2 co~r grad~s are used for making melting pots, known as Mn02+4HCl=Mt£Ch.+Cl!+2H20 crucibles, which are employed for various purposes. Graphite In each of the first three equations, the proportion of the is also used as a lubricant and as a facing material in foundry negative radical that is combined with the metal is increased or work. there is oxidation of the metal or its compound. Also, in each Coal, coke, and charcoal are used mainly as fuels. Lamp of the first two cases, the proportion of the positive element that black is useful as a coloring material. is combined with the negative element is increased and there is a reduction of that negative element. In the third reaction, the 58. Products Obtained by Distillation of Coal-Carbon is amount of the negative element chlorine that is combined with present in coal in two forms, namely, as uncombined carbon an atom of the positive element hydrogen is decreased from one and in volatile compounds that can be separated from the other atom to nothing, and there is reduction of the hydrochloric acid constituents of the coal by distillation. When the coal is heated, to free hydrogen. The substance that is subjected to oxidation the volatile compounds are liberated in the form of gases which in the fourth reaction is the hydrochloric acid, because the pro can be collected. Two of these volatile compounds are illumi portion of the positive element in that compound is decreased. ·nating gas and coal tar. Illumimiting gas remains aaseous at By the same reaction, there is reduction of the manganese diox ordinary temperatures, whereas coal tar becomes li~uid when ide, Mu02, to manganous chloride, MnCI
known as quartz and flint are silicon dioxide, or silica, Si02• 64. Iodine.-Iodine melts and boils at comparatively low Silicon also occurs in -;ilicates, which are compounds containing temperatures. The solid is black and the vapor has a violet besides silicon also oxygen and such metals as potassium and or blue color. This element is only slightly soluble in water. aluminum. These compounds form some of the most common It unites with most metals and with some non-metals, but its and widely distributed rock formations that compose the solid union with hydrogen is very slow. A solution of iodine in crust of the earth. water is an oxidizing agent, although a comparatively feeble Under the influence of air and water, the rocks of the earth one, and a deficiency of iodine in drinking water is apt to result continually disintegrate, forming clay and sand. Clay is a in a prevalence of goiter. fine granular mass produced by the weathering of rocks that OXYGEN COMPOUNDS OF CARBON, SILICON, AND SULFUR contain combinations of silicon and aluminum and are known geologically as feldspars. Sand is also produced by the weather 65. Carbon Monoxide and Carbon Dioxide.-As previously ing of rocks but, since it is formed of harder particles, the grains stated, there are two carbon oxides, namely, carbon monoxide, remain larger than those that compose clay. Sand may consist CO, and carbon dioxide, C02• Both are colorless gases that are of small pieces of feldspar, which are often mixed with small obtained by burning carbon in air, but the product of the com pieces of quartz; or it may consist entirely of small pieces of bustion depends on whether or not the process is completed. quartz, in which case it is called silica sand. Silicon also is an Carbon monoxide is extremely poisonous. I t is a powerful important constituent of cast iron and some kinds of steel. reducing agent and is only slightly soluble in water. It bums ELEMENTARY CHEMISTRY 44 ELEMENTARY CHEMISTRY 45
.mmrw• · 'th a blue flame, the product of the combustion being These silicates give a hardened mixture of cement and water its carbon dioxide. strength because, when the water is mixed with the cement, the Carbon dioxide is a product of all ordinary fires. Also, it is silicates hydrate and form crystals which adhere to one another xhaled by men and animals. Therefore, some carbon dioxide and to bodies that are in contact with the cement. ~ always present in the atmosphere. It is injurious when in too great a concentration, as when many people are congre 68. Sulfur Compounds.-When sulfur burns in air, sulfur gated in a poorly-ventilated room. It is readily soluble in water. dioxide, 502, is usually formed but small quantities of sulfur Carbon dioxide can be condensed into a solid form and is then trioxide, 503, are also produced under certain conditions. Sul known as dry ice. fur dioxide is a colorless gas that has a very disagreeable smell. It is especially poisonous to vegetation and also affects animals 66. Carbonic Acid and Carbonates.- When carbon dioxide is to some extent. It is a powerful bleaching agent. However, its dissolved in water, the solution is known as carbonic acid. bleaching effect is not permanent, because the original color is The reaction may be indicated by the equation gradually restored under the influence of the oxygen in the air. Sulfur trioxide combines with water to form sulfuric acid, as C02 + H~ = H£0a indicated by the equation carbon + tc _ carbonic dioxide wa r - acid 50a + H20 = H<;$04 Therefore, carbon dioxide is sometimes called carbonic acid sulfur + ter _ sulfuric tnox1. "d e wa - act.d gas or carbonic anhydride. Carbonic acid is the common soda water that is used as a beverage. The colder the water, the Thus, sulfur trioxide is the anhydride of sulfuric acid. A small greater is the volume of gas it will dissolve. The gas may be quantity of this anhydride is present in cement. driven off by heating the water, and entirely removed by boiling Sulfuric acid is a dense, colorless liquid of oily consistency. the water. It has a strong attraction for water, and the mixing of these two Carbonic acid is a weak acid and has but little effect on metals. liquids is accompanied by the evolution of considerable heat. However, it reacts with bases to form salts called carbonates. For this reason, water should never be poured into sulfuric acid. Marble, limestone, and chalk are forms of calcium carbonate, H it is desired to mix the two substances, the acid should be CaC03. Also, baking soda is sodium bicarbonate, NaHCOa, poured slowly into the water. Sulfuric acid is destructive to and washing soda is sodium-carbonate crystals, N~C03 • lOH~. all animal and vegetable matter. Also, it unites with most of the bases; and it dissolves many metals while cold and dissolves 67. Silicates.-There is only one binary compound of silicon most of the other metals with the aid of heat. and oxygen. This is silicon dioxide, or silica, 5i02, which is a very bard substance that is found in nature as quartz and flint. ORGANIC CARBON COMPOUNDS
Silica is the anhydride of silicic acid, H25i03• The acid is not 69. Homologous Series.-The carbon compounds that are used, but its salts, which are called silicates, are of great impor of an organic nature are divided into a number of families. All tance. Thus, feldspars are silicates containing aluminum and the compounds of the same family show a strong resemblance other metals such as calcium, sodium, and potassium. Also, to each other in their chemical composition and chemical proper cement contains t)Vo kinds of calcium silicate; namely, tricalcium ties, and a family of compounds is said to form an homologous silicate, 3Ca0 . Si02, and dicalcium silicate, 2Ca0 . 5i02• E.eries. BB 2118--4 ELEMENTARY CHEMISTRY 46 ELEMENTARY CHEMISTRY 47
70. Hydrocarbons and Bitumens.-All the organic carbon these two classes of substances is that paraffin compounds are compounds contain hydrogen besides the carbon. There are a greasy and asphalt compounds are sticky. very large number of compounds that contain only these two clements and are called hydrocarbons. The hydrocarbons occur 71. Paraffin Series.- The simplest homologous series of chiefly in mixtures that are collectively known as bitumens. hydrocarbons is that known as the paraffin series. The names Some bitumens occur in nature as solids, liquids, or gases; and and chemical formulas of the first sixteen compounds of this other bitumens are artificially prepared by the distillation of series are given in Table VI. Each succeeding compound is bituminous coal. All bitumens are soluble in carbon disul formed from the preceding one by adding one atom of carbon phide, cs2.. and two atoms of hydrogen to the molecule. In other words, The mixtures of hydrocarbons in bitumens are so complex, the difference between any two successive compounds is the and the various compounds contained in those mixtures are so quantity CH2. This addition of CH2 may be continued in a numerous, that it is very difficult to separate them into indi similar manner for other compounds of the series. Paraffin vidual compounds. However, the characteristics of a particu molecules containing over ninety atoms of carbon have been lar bituminous mixture are determined largely by the predomi produced. The paraffin compounds whose molecules contain nance in it of compounds belonging to one homologous series, or not more than four atoms of carbon are gases at ordinary temper family, of hydrocarbons. It is therefore customary to classify atures; the compounds whose molecules contain from five to bitumens, according to the predominating homologous series, fifteen atoms of carbon are liquids; and the compounds whose as para!fi1~s and asphalts. The physical difference between molecules contain more carbon are solids. Methane, CH4, which is also known as marsh gas and as fire TABLE VI damp, is produced during the slow decay of organic matter. COMPOUNDS OF PARAFFIN SERIES It is, therefore, found in considerable quantities in stagnant
Nam~ o( Compound Formula Characteristic pools, bogs, and coal mines; and it is also produced in the treat ment of sewage. This gas bas a fairly high fuel value. Certain Methane...... CH. Gas mixtures of methane and air are explosive when ignited. Ethane...... C,HG Gas Many of the liquid and solid paraffins are used as water Propane...... CJis Gas proofing agents, especially in waterproofing concrete structures Butane...... c.HJO Gas and in producing waterproof paper. Paraffins are also used in Pentane...... C.Jla Liquid Hexane...... CJI,. Liquid commercial waxes, as lubricants, and for many other purposes. Heptane...... C,H11 Liquid The liquid paraffins are mineral oils. Octane...... CJI,s Liquid 72. P roducts Obtained by Distillation of Crude Petroleum. Nonane...... C.Hto Liquid Decane...... C,oHn Liquid Crude petroleum, or crude oil, is a heavy, yellowish-green Undecane...... CuHt• Liquid liquid that is found in pools in the earth. It consists of solid, Dodecane...... CttHtc Liquid liquid, and gaseous hydrocarbons mi.xed or dissolved in one Tridecane ...... C,Jiu Liquid another in various proportions. The gaseous hydrocarbons Tetradecane...... C,JI,. Liquid readily escape at ordinary temperatures. In the distillation of Pentadecane ...... C,Jln Liquid Hexadecane ...... C,Jiu Solid petroleum, the distillate that is obtained at temperatures below Etc...... 150° C. is gasoline, and the distillate that is obtained at temper atures between 150° and 300° C. is kerosene. If the petroleum ELEMENTARY CHEMISTRY ELEMENTARY CHEMISTRY 49 48 . f th paraffin class, the residue consists of heavy lubricating 75. Glycerine.-0ne of the alcohols obtained from a paraffin 0 JSil gr:ases, and paraffin wax; but, if the petroleum is of the by replacing more than one hydrogen atom with an equal num 0 s \a1t class, the residue is a black mass that consists of solid ber of hydroxyl radicals is glycerine. This compound is derived ~}~ocarbons and is known ~ asphalt. There is no dist~cti_ve from propane, CJfs. by replacing three of the hydrogen atoms, boundary line between gasoline and kerosene, the arb1tranly and its formula is C3fls(0//)3. It is a clear, colorless, syrupy fixed boiling point of 150° C. being used as the division line; liquid and has a remarkable attraction for water. both liquids are more or less indefinite mixtures of many The alcohols have the same chemical properties as inorganic chemical compounds, and have no special definite chemical bases. When nitric acid, HNOa, is added to glycerine, the formulas of their own. This is true also of the paraffins and reaction is as indicated by the equation asphalts that remain after the more volatile products have been removed by distilla~ion. However, asphalt is not always CJ[~(OH)3 + 3HNOs = CaH~(/1:03)3 + 3H20 . + nitric . obtained by distillation, since it is found in solid deposits of g1 ycenne .d = mtroglycerine + water more or less pure hydrocarbons; asphalts from such solid aCI deposits are collecti..;ely known as tzatiue asphalts. Asphaltic The compound whose formula is C3H s(N03)a is the powerful bitumens are widely used in road building, in roof coverings, explosive known as nitroglycerine. This is the substance that and for many other purposes. gives dynamite its explosive properties. 73. Coal-Tar Pitch.-As previously explained, coal tar is a distillate obtained in the distillation of coal. If the coal tar 76. Aldehydes.- Vlhen an alcohol is oxidized by the addition itself is broken up into its component products by distillation, of oxygen, two atoms of hydrogen combine with one added the residue is a heavy, black substance known as coal-tar pitch. atom of oxygen to form water and a compound called an alde This substance is used for waterproofing purposes, for road con hyde. In the case of methyl alcohol, for example, the reaction struction, and as a coating on steel and iron water pipes to is as follows: prevent corrosion, or rusting, of the metal. 2CH:{JH + Oz = 2CH
for which C17Ha5 . COOH. Steanc acid occurs m taJiow and It IS obtainable in the form of a powder which is sometimes mixed 80. Benzenes.-The benzenes constitute another homo with cement in order to make concrete more water-tight. As logous series of hydrocarbons. · The simplest compound of this glycerine is usually found chemically combined with stearic series is benzene, or benzol, CJfG; and the next one is toluene, acid, this acid must be freed from the glycerine before it is used or toluol, C1Ha. Benzene is a derivative of coal tar. It is a as a waterproofing substance. colorless liquid that is highly inflammable. Fatty acids react with alcohols to form organic salts called The substance known as phenol, or carbolic acid, is obtained esters. Such reactions are simil~r to those that take place by replacing one atom of hydrogen in benzene by the hydroxyl
between inorganic acids and bases. radical OH. Thus, the formula for carbolic acid is CJ[50H. This flCid is extremely poisonous. 78. Other Derivatives of Pa.raffins.-The substances known It is also possible to obtain acids that are similar to fatty as ethers are derived from alcohols by substituting a radical acids by replacing one atom of hydrogen in benzene by the for the hydrogen in the hydroxyl radical. For example, if radical COOH. For instance, benzoic acid has the formula the radical CHa is substituted for the last hydrogen atom in CJ[,COOH. AJso, if one of the hydrogen atoms in benzoic acid methyl alcohol, CHaOH, the resulting product has the formula is replaced by the hydroxyl radical, the resulting product is CHI)CH3 and is known as methyl ether. Likewise, ethyl ether salicylic acid, the formula for which is C6H4(0H)COOH. has the formula C2H&OCJ-h Ethyl ether is a very volatile liquid and is inflammable. When the term ether is used without 81. Naphthalene.- The largest single constituent of coal qualification, it is w1derstood that ethyl ether is meant. tar is naphthalene, the formula for which is C1oll8 . Various It is also possible to replace one or more of the hydrogen derivatives of naphthalene may be produced by replacing one atoms in a paraffin by means of an equal number of atoms of atom of hydrogen by an atom of another element or by a radical. chlorine or iodine. Thus, if three atoms of hydrogen in methane, Thus, the substance that is known as alpha naphthylamine, CH4, are replaced by chlorine atoms, the result is chloroform, or a-naphthylamine, has the formula C1oH:NH2• CHCL3; and, if iodine is substituted, the result is iodoform, CH1 3• 79. Acetylene.- The paraffin series is not the only homo 82. Carbohydrates.-Many of the carbon compounds are logous series of hydrocarbons in which the formulas of the called carbohydrates because the proportions of hydrogen and oxygen in such compounds are the same as in water; in other successive compounds differ by the quantity CH~. There are also several other such series, but the first compound of each words, the number of hydrogen atoms is twice the number of series has a different composition. In one series, the first oxygen atoms. A few of the more commonly known carbo compound has the formula C2H2 and is the gas known as acety hydrates are starch, C6H1o05 ; dextrose, or grape sugar, C6HdJ6; lene. This gas burns with a very bright flame and, therefore, and sucrose, or cane sugar, C12H'120u. is useful for illuminating construction work that is carried on at night. Also, its combustion in oxygen produces a very high temperature, and a mixture of oxygen and acetylene gas is used to produce the oxyacetylene flame which finds extensive applica tion in welding or cutting metals, especially steel and iron. ELEMENTARY CHEMISTRY ELEMENTARY CHEMISTRY 53 52
ALKALI METALS METALLIC ELEMENTS AND THEIR COMPOUNDS 84. General Characteristics of Alkali Metals.-The alkali CLASSIFICATION OF METALS metals are lithium, sodium, potassium, rubidium, and cesium. 83. The various elements rriay be divided into periods on AU these metals are :;oft. and ru·e light in weight. They are th basis of their atomic numbers. There are several methods easily melted and volatilized; that is, they change in form from ofemaking this division, but the most common method is as solid to liquid and also from liquid to gas at comparatively low follows: Period 1 consists of the two elements, hydrogen and temperatures. Their hydroxides are soluble in water and unite helium, whose atomic numbers are 1 and 2. Period 2 consists with all acids to form salts that can be decomposed only with of the elements with atomic numbers between 3 and 10; period difficulty. The two most common alkali metals are potassium 3 consists of the elements whose numbers are between 11 and and sodium. Both potassium and sodium oxidize quickly when 18; period 4, of those with numbers between 19 and 36; period 5, exposed to moist air. Cesium is used in photoelectric tubes of those with numbers between 37 and 54; period 6, of those because it reacts to changes in intensity of light. with numbers between 55 and 86; and period 7, of the remaining six elements. 85. Potassium.-Potassium occurs in nature in combina The elements may also be classified, according to their tion with various other elements. It is a constituent of most characteristic properties, into such classes as inert gases, feldspars and of some micas; both feldspars and micas are com alkali metals, and alkaline-earth metals. If an analysis is binations of silicates of potassium and other metals. Saltpeter made of the characteristics of the elements in each period, it is is potassium nitrate, KJ\"03, and potash is potassium carbonate, found that there is a relation between the elements that occupy K£03. Other important sources of potassium are the double corresponding positions in the various periods. The last salts of potassium and magnesium that are known as carnallite element in each period, or the element that has the highest and kainite. Potassium oxide combines with water to form atomic number, is an inert gas. The first element in each potassium hydroxide, KOH, which is often called caustic potash. period, or the element with the lowest atomic number, is an Saltpeter and potash are indispensable ingredients of most alkali metal; the only exception is in the first period, in which commercial fertilizers, and kainite also is used as a fertilizer. the gas hydrogen is the first element. The second element in The substance known as lye is a solution of potash. It is used each period is an alkaline-earth metal, except in the first period, as a disinfectant; and, in combination with an aluminum com in which the inert gas helium is both the second and the last pound known as alum, it is sometimes employed in waterproofing element. Also, various pairs of similar metals, such as the so concrete and in purifying water. called precious metals silver and gold, lie at equal distances from the ends of their respective periods. 86. Sodium.-sodium, in combination with other elements, In the following articles, some metals are grouped according is abundantly and widely distributed in nature. As sodium to their characteristic properties and other metals are grouped chloride, A"aCl, which is common salt, sodium is found in according to the periods in which they belong because of their enormous quantities both in sea water and in deposits of rock atomic numbers. Where the metals are grouped according to salt. Also, large amounts of sodium are found in South periods, the order in which they are mentioned is such that America in the form of sodium nitrate, NaN03, which is some l>imilar metals are placed together. times called Chile saltpeter. Other well-known compounds of sodium are caustic soda, or sodium hydroxide, NaOH; soda ash, 54 ELEMENTARY CHEMISTRY ELEMENTARY CHEMISTRY 55
or sodium carbonate, Na2COJ; washing soda, Na£;03 • 10H20; hygroscopic, as it absorbs moisture from the air. It is frequently baking soda, or sodium bicarbonate, NaHC03 ; Glauber's salt, applied to the surface of an earth road or to the surface of new or sodium sulfate, N~S04. lOH20; and water glass, or sodium concrete in order to keep the surface damp. It is also applied silicate, NaSiOa. Soda ash is extensively used in the purifica-· to roads to prevent the formation of ice or to thaw ice already tion of water, and water glass is often used to prevent fresh formed. concrete from drying out too rapidly. Sodium vapor is used Large blocks of limestone and marble are extensively used in some electric lamps. in buildings and other large engineering structures. Also, calcium carbonate in the form of crushed limestone is used ALKALINE-EARTH METALS AND BARTH METALS in concrete and as a flux in the proCess of separating iron from 87. Basis of Classification.-The metals whose compounds the impurities in its ores. The substances known as gypsum constitute the ctust of the earth are known as earth metals. and plaster of Paris are combinations of calcium sulfate and
By far the most important of these metals is aluminum. Th~re water; the formula for gypsum is Ca504 • 2H20 and that for is also a group of metals that resemble the alkali metals in plaster of Paris is (2Ca504)Hz(). A mixture of plaster of Paris some respects and the earth metals in other respects. The and alum is known as Keene's cement. metals of this intermediate group are therefore called alkaline earth metals. Calcium and magnesium are the most imoortant 89. Magnesium.-Magnesium is fairly abundant, but is alkaline-earth metals, but beryllium, barium, and st;ontium almost invariably associated with calcium. Thus, although are also of importance. magnesium carbonate, MgC03, occurs alone in the mineral known as magnesite, it is usually found combined with calcium 88. Calcium.-calcium is comparatively light in weight, carbonate, as in dolomite and other magnesian limestones. but is fairly hard. It is oxidized slowly by moist air. It Magnesium in the form of a silicate is an ingreclient of asbestos, is found in nature as the carbonate, CaC03, in many minerals, hornblende, olivine, talc, and meerschaum. Magnesium chloride, such as limestone, marble, and chalk. Calcium also occurs MgCh, is found in sea water. in the form of calcium phosphate, or tricaJcium phos Metallic magnesium is readily oxidized in moist air. It burns phate, Caa(P04)2; in the form of the silicate, Ca5i03 ; in with a dazzling white light and for this reason was formerly the form of fluorspar, CaF2; and in the form of hydroxy apatite, used in flashlight photography. Magnesium oxide, MgO, 3Caa(P04)2 . Ca(OH)2. This element is an important constit which is often called magnesia, is highly refractory and is used uent of the bones of animals and the shells of oysters. to a great extent in crucibles and in linings for electric furnaces. Many compounds of calcium are very widely used in con This oxide reacts slowly with water to form magnesium hydrox struction work and also for other purposes. Calcium oxide, ide, Mg(OH)2. Magnesium is the main ingredient of several CaO, is the substance known commercially as quicklime or burnt alloys, or mixtures of metals, which are used for parts of lime, or merely as lime. As lime is highly refractory, or resis structures that must be strong and yet light in weight. Such tant to heat, it is used in the construction of crucibles. Calcium alloys also contain aluminum, copper, and manganese. hydroxide, Ca(OH)2, is generally known as hydrated lime or slaked lime, being produced by slaking quicklime by mixing it 90. Beryllium.-The metal beryllium, which was formerly with water. Hydrated lime is used extensively in the mortar for known also as glucinum, is found combined with aluminum in brick masonry; and both quicklime and hydrated lime are used the form of a silicate in beryl. Emeralds are specimens of beryl in the purification of water. Calcium chloride, CaC/2, is that are colored green because of the presence of a small per- ELEMENTARY CHEMISTRY 56 ELEMENTARY CHEMISTRY 57 centage of chromium silicate. Beryllium also occurs as a ture is utili7.ed in welding steel rails and pipes or other steel fluoride having the formula BeF2. 2KF. . products. Beryllium is very light in weight. Since it is comparatl~eiy 93. The aluminum ore bauxite is an important ingredient of strong and does not oxidize or melt so readily as magnes1um, alumina cement, which develops high strength much more it is advantageously used in light-weight alloys with copper, rapidly than does ordinary portland cement. Also, pure nickel, and iron. aluminum oxide, or alumina, Alz(J3, is extremely hard and is 91. Barium and Strontium.-Both barium and strontium used as a polishing material under the names corundum and are found as carbonates and as sulfates. A mixture of t he car emery. The substance known as alundum, which is produced bonates of barium and strontium is used as a coating on the by melting alumina in an electric furnace, is highly refractory metallic filaments in certain types of radio tubes. and is used for crucibles. Aluminum is a constituent of the substances known as alums. One kind of alum, which is gen 92. Aluminum.-Aluminum is one of the most abundant erally called aluminum sulfate or filter alum and has the formula and widely distributed elements, ranking next to oxygen and A~(S04)a . 18Hz(), is extensively used in the purification of water. silicon. It does not occur free in nature. However, it is found Alloys of aluminum with other metals are used to a con as a silicate in all clays and in many minerals; as an oxide and siderable extent for various purposes, especially where it is a hydroxide; and in other combined forms such as cryolite, desirable to have a material that is strong and light in weight 3NaF . AlF3• The principal commercial source of aluminum and that resists corrosion. Several different aluminum alloys is the ore called bauxite, the formula for which is A~3. 2Hz(). containing small percentages of copper, silicon, manganese, Aluminum is one of the lightest of the common metals. It magnesium, and chromium are used in the construction of air has high tensile strength, it can be hammered or drawn into craft, automobiles, railroad trains, buildings, and bridges. various shapes, and it melts at a temperature of slightly over Such alloys are used also for the cables in long lines for trans 1,200° F. When aluminum is exposed to the air or is immersed mitting electric current. An alloy known as aluminum bronze, in dilute nitric or sulfuric acid, it immediately becomes coated which consists of copper and about 10 per cent of aluminum, is with a thin layer of aluminum oxide, Alz(Ja, which protects it also used in aircraft. from further attack. However, it is dissolved by dilute hydro METALS IN FOURTH PERIOD chloric acid; also, it reacts with a boiling solution of potassium hydroxide or sodium hydroxide to form aluminates. In uniting 94. Iron.-Iron is the most important and also one of the with a base, aluminum resembles the non-metallic elements; most common of the metals. It is not found in the pure state, but, as it also unites with acids to form salts, it is generally except "in meteors, but is obtained from several different ores. classified as a metal. The principal ores are hematite, Fe203 ; magnetite, Fe£)4; Aluminum is a powerful reducing agent, as it has a very limonite, 2Fez(J3 • 3Hz(); and siderite, FeC03• Iron also occurs great affinity for oxygen. If a mixture of powdered aluminum as pyrite, FeS2, but the sulfur bas an injurious effect on the iron and iron oxide is ignited, aluminum oxide and iron are formed, in this compound. as indicated by the following equation: Iron is used commerciaUy in three well-known materials, namely, cast iron, wrought iron, and steel. Wrought iron 2Al+Fez0a= Alz(Ja+2Fe is nearly pure iron. Cast iron contains a comparatively The reaction produces an enormous amount of heat, which large amount of carbon and also small percentages of other causes the iron to be in a fluid form. . This property of the mix- elements, such as silicon, sulfur, and phosphorus. Steel ELEMENTARY CHEMISTRY ELEMENTARY CHEMISTRY 59 58 . mi.xture of iron with carbon and various combinations of the 97. Copper.-Large masses of native copper are found in IS a 'li . k 1 chr . f llowing elements: SJ con, rue e , manganese, ormum, the region around Lake Superior and in other JocaJities. Copper t~ngsten, va~dium, sulfur, and phosphorus. T_here is ~lso an also occurs abundantly as sulfides, in which it is usually associ alloy of iron wtth copper and molybdenum. This alloy lS used ated with iron and other metals; as carbonates; and as cuprous for culvert pipe. oxide, C1,£J. It possesses considerable strength, and it may be hammered into sheets or drawn into wire. Because of its 95. Wrought iron can be rolled, forged, and welded, but high conductivity of electricity, it is extensively used for wires cannot be cast. I t is comparatively strong and tough, and and cables that carry electric currents. Also, since copper does not rust or corrode readily. Cast iron melts at a tempera offers considerable resistance to the action of acids that do not ture of a little over 2,000° F. and can be readily cast in molds of contain oxygen, it is used for kettles, roof covering, ships' any desired shape. However, it is too brittle to be rolled or bottoms, and coins. A coating of copper is often deposited forged and is apt to fracture if subjected to shock. Steel has on another metal by copper-plating. greater strength than wrought iron and can be rolled, forged, Copper is the principal ingredient of many alloys. Thus, welded, and cast in molds. Also, its properties can be readily brass is an alloy of copper and zinc; bronze is an alloy of copper, changed to a considerable degree by heat treatment. However, tin, and zinc; aluminum bronze consists of copper and alumi steel rusts more easily than does wrought iron or cast iron. num; and phosphor bronze consists of copper, lead, tin, and a Both iron and steel are strongly attracted by magnets and can little phosphorus. Also, monel metal, which is much used for be magnetized. sheet-metal work, contains about equal proportions of copper Ferric oxide, Fe20 3, is an important ingredient of mineral and nickel; and German silver, or nickel silver, contains 50 paint. Also, in one method of waterproofing concrete, use is per cent of copper, 25 per cent of nickel, and 25 per cent of zinc. made of finely powdered iron and a chemical which hastens Copper sulfate is used extensively in the purification of water rusting and is usually sal ammoniac, NH.Cl. The following iron to destroy t roublesome vegetable growths, known as algae, and salts are widely used in the purification of water: copperas, or for various industrial purposes. ferrous sulfate, FeS04 • 7H.J); ferric chloride, FeCla; ferric sul fate, Fe,(S04) 3 ; and chlorinated copperas, Fe2(SO.)aFeCl3. 98. Nickel.-The principal minerals containing nickel are garnierite, which is a silicate of nickel and magnesium; niccolite, 96. Manganese.-Manganese is found chiefly as pyrolu the formula for which is NiAs; and pentlandite, which is a sul site, Mn02 ; braunite, M11.JJs; and manganese spar, MnCOa. fide of nickel, copper, and iron. Nickel tarnishes slightly in air, This element resembles iron in its tendency to combine with but rusts very slowly. The electrodes in some t ypes of radio carbon at a high temperature. It is an important constituent tubes are made of nickel. Also, a coating of nickel is often of manganese steel, which is an alloy of iron, manganese, and deposited on another metal by nickel-plating. carbon. Such steel is used extensively for parts of railroad Nickel is used in several important alloys. Thus, steel track that are subjected to severe wear and also for the jaws of containing a small percentage of nickel is a strong material stone-crushing machines. An alloy of copper and manganese, that is used in long bridges; and steel containing a high per known as manganese bronze, has great strength and will not centage of nickel is used where high resistance to corrosion is corrode easily. Potassium permanganate, ICM110., is used as required, as in boiler tubes and valves for gas engines. Invar, an oxidizing agent in the purification of water anc.i for various which is an alloy of iron with a comparatively large percentage other purposes. of nickel and very little carbon, is used extensively for precise ELEMENTARY CHEMISTRY 60 ELEMENTARY CHEMISTRY 61 measuring tapes and bars because changes in temperature have Cobalt resembles nickel in many respects. It is magnetic very little effect on the dimensions of a mass of this material. and is therefore used in an alloy steel for magnets. Also, a Monel metal and German silver contain large percentages of material known as stellite, which is an alloy of cobalt, chromium, nickel, and coinage nickel consists of about 75 per cent of copper and tungsten, is used for high-speed cutting tools, as this alloy and 25 per cent of nickel. retains its hardness and strength even at a red heat. 99. Chromium.-The two princi~al sources of chromium are Selenium bears a marked resemblance to sulfur. In a metallic chromite, or chrome iron ore, Fc(Cr02)2, and crocoisite, or lead form, it conducts electricity to some extent and it is used in chromate, PbCr04 • Chromium has a pleasing color and great electronic cells which react to changes in the intensity of light. hardness, and it oxidizes very slowly in the air, even when heated. It is therefore used extensively as chromium-plating. METALS IN PIFTH, SIXTH. AND SEVENTH PERIODS Chrome steel is an alloy of iron, chromium, and carbon that 102. Tin.-The most important tin ore is cassiterite, or is very hard and is used principally for armor plates and pro stannic oxide, Sn02. Tin is extensively used as tin-plating jectiles. There are also several other stP.els in which chromium on steel for use as roof covering and in cans. It is also used as and other metals are combined with iron and carbon. Thus, plating on the interior of copper vessels. The most important chrome-nickel steel is used in automobiles and aircraft for parts alloys of tin are bronze; solder, which contains tin and lead; and that are subject to severe wear or great shocks; chrome-vana babbitt metal, which consists of tin, lead, antimony, and copper. dium steel is used for shafts, piston rods, tubes, and wire; and a steel containing chromium, vanadium, and tungsten is valuable 103. Lead.-Most of the lead that is used commercially is for high-speed cutting tools. Some aluminum alloys that are obtained from galena, or lead sulfide, PbS. Lead is used for used for structural work contain a small percentage of chromium. pipes of small diameter and for the plates in storage batteries. 100. Zinc.-The chief source of zinc is zinc blende, which is Also, the oxide, Pb.,04, which is known as red lead, and the an ore consisting mainly of zinc sulfide, Z11S; but much of this carbonate, PbC03, which is known as white lead, arc used in metal is also obtained from ores containing the carbonate, paints. The substances called litharge and massicot arc forms of lead monoxide, PbO. Alloys containing lead arc phosphor ZnC03, the silicate, Ztr~i04, or the oxide, ZnO. Zinc is exten sively used as a coating on steel to form galvanized iron. It is bronze, solder, and babbitt metal. Also, the metal used for also used in the form of sheets. The most important alloys type is composed of lead and antimony. that contain zinc are brass, bronze, and German silver. Zinc oxide,ZnO, is used in paint: and zinc chloride,ZuCl2, is employed 104. Cadmium and Mercury.-Cadmium is generally found as a preservative of timber and as a flux in soldering. The associated with zinc, and then only in small quantities. An sulfide. ZuS, or the silicate, Ztr,SiO., is sprayed on the surfaces important use of cadmium is in alloys that melt at a compara of tubes used in television to form a screen on which the images tively low temperature. This metal is also used in automobiles are projected. as plating on bolts, nuts, and other small parts and in alloys with nickel or silver for bearings. 101. Vanadium, Cobalt, and Selenium.- Vanadium is a Mercury occurs both free and as cinnabar, which is mercuric comparatively rare element that is found in c1ay, coal, and a sulfide, HgS. It is a liquid at ordinary temperatures and is few minerals. A small percentage of vanadium is sometimes very heavy. It is therefore used in barometers and other used in steel, in order to increase the strength and hardness of instruments for measuring pressure in liquids and gases. Be the steel. cause of its uniform changes in volume with variations in BB 211B-S 62 ELEMENTARY CHEMISTRY ELEMENTARY CHEMISTRY 63 temperature, mercury is also used in thermometers. Mercury but is seldom used for electric wiring because of its cost. Since vapor is used in some electric lamps. Am~gams, or all~ys it offers considerable resistance to alkalies and to a11 acids except in which mercury is a constituent, are readdy formed wtth nitric acid, silver is extensively used as a plating on other metals, most of the common metals; iron and platinum are notable especially for tableware. exceptions. The chief compounds of mercury arc mercurous Gold is usually found in small quantities in the free state, as chloride, Hgz(;~. which is the medicinal substance known as it does not readily combine with other elements, but small calomel; and mercuric chloride, or bichloride of mercury, HgC~, quantities are found in ores of iron, lead, and copper. It is very which is a very poisonous antiseptic. malleable and ductile and is extensively used in the form of extremely thin sheets known as gold leaves. Also, gold makes a 105. Molybdenum and Tungsten.-The chief sources of desirable plating on other metals. molybdenum are wulfenite, PbMo04, and molybdenite, MoS2. The electrodes of some radio tubes are made of molybdenum. 108. Platinum, Tantalum, and Thorium.-Platinum is This element is also an important constituent of an alloy with found associated with other metals in the form of nuggets. Fine iron and copper, which is used for culvert pipe, and it is an platinum wires are commonly used in telescopes of surveying ingredient of some steel. . . instruments. This element is also used in electrical apparatus Tungsten is found in a number of different_ mmerals, a few and for crucibles. of which are wolframite, (Fe, Mn)WO.; scheehte, CaWO.; and Tantalum occurs in nature in a few comparatively rare stolzite PbW04• This element is very hard and melts at a minerals. As this element melts at a high temperature, the high t~mperature. It is used for filaments in electric-li~ht electrodes in some radio tubes are made from it. bulbs and radio tubes. Tungsten is also an important constitu Thorium occurs mainly as a silicate. It is combined with ent of steel that is used for high-speed cutting tools, as such tungsten in the filaments of some radio tubes. steel retains its hardness when hot. 106. Antimony and Bismuth.-Some antimony is found free CHEMICAL EQUATIONS in nature, but the principal source is stibnite, or antimony tri 109. Balance in Equations.-When a chemical equation is sulfide, Sbt53• This element is a constituent of several alloys, written to indicate the changes that take place during a reac such as babbitt metal and the metal used for type. The anti- tion, the total number of atoms of any element should be the mony serves as a hardener. . same in each member of the equation. In other words, the Bismuth occurs in nature both free and combmed. The equation should be balanced. Two examples of balanced oxide, Bi?_03, and the sulfide, Bi~3, are the most common com equations follow: pounds. The principal use of bismuth is in various alloys that 2H2+D2=2H£J melt at a comparatively low temperature. One of these alloys, 2NaOH+H2COa=NazC03+2H.JJ which is known as Wood's metal, contains about 50 per cent of bismuth, the remainder being lead, tin, and cadmium. Both To determine whether or not an equation is balanced, the bismuth and antimony expand on solidifying. total number of atoms of each element in each member of the equation is counted, and the two values for each element are 107. Silver and Gold.-silver occurs free in nature and is compared. The procedure in investigating the first equation also found in several ores, most of which contain other metals in for balance is as follows: In the left-hand member there are addition to silver. It is an excellent conductor of electricity four atoms of hydrogen, because there are two molecules of ELEMENTARY CHEMISTRY 64 ELE MENTARY CHEMISTRY 65 that element and each molecule contains two atoms; and in carbonic acid, the required weights of these two substances are the right-hand member there are likewise four atoms of hydro in the ratio of 2 X 40 =80 to 62. In other words, if it is desired gen, because there are two molecules of water and each such to use 80 pounds of sodium hydroxide, it would be necessary to molecule contains two atoms of hydrogen. Also, it is evident use also 62 pounds of carbonic acid. For 100 pounds of sodium that each member of the equation contains two atoms of oxygen. hydroxide, the corresponding weight of carbonic acid would be In the case of the second equation, the left-hand member con 100 tains two atoms of sodium in the two molecules of sodium 80 X 62 = 77.5 pounds. hydroxide, and the right-hand member contains two atoms of sodium in the molecule of sodium carbonate. The total num 111. Weights of Substances Produced by Reaction.-The ber of atoms of oxygen in the left-hand member is 5, or 2 in the relative weights of the substances that are produced by a two molecules of sodium hydroxide and 3 in the molecule of chemical reaction can also be determined from the molecular carbonic acid; and the number in the right-hand member is also weights of those substances and the number of molecules of each S, or 3 in the molecule of sodium carbonate and 2 in the two substance. As an illustration, let it be desired t-0 find the rela molecules of water. Also, there are two atoms of hydrogen in tive weights of sodium carbonate and water produced by the the two molecules of sodium hydroxide and two more in the reaction between sodium hydroxide and carbonic acid. As the molecule of carbonic acid, or a total of 4 such atoms in the left equation in the preceding article indicates, there are one mole hand member; likewise, there are 4 atoms of hydrogen in the cu1e of sodium carbonate and two molecules of water. Also, two molecules of water in the right-hand member. Finally, the approximate molecular weight of sodium carbonate, Na2C03, there is one atom of carbon in each member. is 2X23+12+3X16=106 and that of water is 2X1+ 16 = 18. Hence, the relative weights of the two substances are 106 and 110. Weights of Substances Required for Reaction.-The 2X18=36. If 80 pounds of sodium hydroxide are combined relative weights of the substances that are required for a certain with 62 pounds of carbonic acid, the substances produced wou1d chemical reaction can be determined from the equation for be 106 pounds of sodium carbonate and 36 pounds of water. that reaction and the molecular weights of these substances. From 100 pounds of sodium hydroxide and the corresponding In computing the molecular weight of a substance, it is usually weight of carbonic acid, the products would be ~o.; X 106 = 132.5 satisfactory to use approximate values for the atomic weights of pounds of sodium carbonate and WX36=4S pounds of water. the elements, as explained in Art. 16, rather than the extremely It will be noticed that, when 80 pounds of sodium hydroxide accurate values given in Table I. Thus, in order to find the unite with 62 pounds of carbonic acid, the total weight of these relative weights of sodium hydroxide and carbonic acid that are materials is 142 pounds; and the total weight of the products needed to produce sodium carbonate and water, the first step of t he reaction is 106+36, or also 142 pounds. In general, the is to write the "chemical equation, which is sum of the relative weights of the substances in one member of a chemical equation must equal the sum of the relative weights 2NaOH+ H2COa=Na£0a+2H20 of the substances in the other member. This law is sometimes The next step is to find the molecular weight of each substance. expressed by stating that the weight of matter after a chemical The approximate molecular weight of sodium hydroxide, NaOH, change is the same as the weight before the change. is 23+1 6+1 =40; and the approximate molecular weight of
carbonic acid, H£03, is 2X1+ 12+3X16 = 62. Since two molecules of sodium hydroxide combine with one molecule of ELEMENTARY CHEMISTRY Serial 5367 Edition 1
EXAMINATION QUESTIONS
Notice to Students.-St11dy the. Ius/rue/ion Paper thorortghly brfore ''Oil attempt to OIIS (1) What is a chemical element? (2) What is a chemical compound? (3) The formula for a certain substance is Ca3 (P04)2. Write the full names of the various elements of which that sub stance is composed. Also, state how many atoms of each of these elements there are in a molecule of the substance. (4) Write the chemical formula for each of the following substances: (a) hydrochloric acid, (b) ammonia, and (c) sul furic acid. (5) The two binary compounds of mercury and chlorine have the formulas HgCl2 and Hg2Cl2, respectively. Which of these two compounds is mercurous chloride and which is mercuric chloride? (6) The equation for a certain reaction is as follows: 2FeCia+SnCI2= 2FeCI2+SnCl4 Wbich element is oxidized and which element is reduced? (7) When litmus was added to a certain colorless solution, the solution turned red. \Vas the solution acid or alkaline? (8) State whether each of the following pH values indicates acidity or alkalinity: (a) 12; (b) 4.5; and (c) 7.2. 2 ELE~lEN'TARY CHEJ\IISTRY (9) (a) What is the fonnula for hydrated lime? (b) How is this substance produced? (10) 'Yhat is meant by a hygroscopic substance? (11) Give the names of the elements that make up each of the following alloys: (a) bronze and (b) invar. In each of the following questions, use the nearest whole number for the atomic weight of each element and indicate the calculations for obtaining your answer. (12) Calculate the molecular weight of the compound whose fonnula is given in Question 3. Ans. 310 (13) How many pounds of phosphorus are contained in 100 pounds of the substance considered in Questions 3 and 12? Ans. 20 lb. (1-!) How many grams of solute should be used to produce a liter of a normal solution of copper sulphate, CuSO~? Ans. 80 (15) (a) How do bitumens occur in nature and how are they classified? (b) Give the formulas of ethyl alcohol and methyl alcohol and state how each is obtained. Mail your work on this lesson as soon as you have finished it and looked it over carefully. DO N OT HOLD IT until another lesson is ready.